1966 327-300hp Spark Plugs

[Larry M.]

I had my car at an idle for 10 minutes and developed a skip, it seems a spark plug fowled out. I have AC45 plugs in it now, someone told me to use AC45S plugs. What is the advantage of AC45S vs AC45. And is it safe to use the AC45S in my 327-300hp engine? Thanks for any info.........

[Jim C.]

Re: 1966 327-300hp Spark Plugs

Hey Larry,

I don't have any reference materials in front of me right now, but I think the 1966 327/300 motors were running AC 44 plugs. I've had them in my 1966 327/300 for about three years now with no problems. I check them every spring, keep them clean, and my car seems to be running fine with them. I don't remember if AC 45 plugs are recommended or not. Are the 45 plugs the functional equivalent of the 44 plugs?

Jim C.

[Joe L.]

Re: 1966 327-300hp Spark Plugs

I had my car at an idle for 10 minutes and developed a skip, it seems a spark plug fowled out. I have AC45 plugs in it now, someone told me to use AC45S plugs. What is the advantage of AC45S vs AC45. And is it safe to use the AC45S in my 327-300hp engine? Thanks for any info.........

Larry-----


The "S" suffix AC spark plugs have an extended tip to help resist fouling. You should be able to use them in your engine with no problem. If it were me, though, I'd use the Champion equivalent.

[Joe C.]

Re: 1966 327-300hp Spark Plugs

Hey Larry,

I don't have any reference materials in front of me right now, but I think the 1966 327/300 motors were running AC 44 plugs. I've had them in my 1966 327/300 for about three years now with no problems. I check them every spring, keep them clean, and my car seems to be running fine with them. I don't remember if AC 45 plugs are recommended or not. Are the 45 plugs the functional equivalent of the 44 plugs?

Jim C.

AC43 plugs were specified for "off road" use
AC44 plugs were specified for all around driving
AC45 plugs were specified for sustained low speed driving

AC44 plugs are the best choice, and I run them in my engine, with no issues. They are, of course, long discontinued but can be found at swap meets, etc.
The best choice with today's availability is the AC R45, rather than the R43. You should be able to use extended tip plugs AC R45S with no issues. If you are uncertain, then index them with the electrode opening facing 6 o'clock (toward from the piston crown).

[Jim C.]

Re: 1966 327-300hp Spark Plugs

Hey Joe,

What is the Champion equivalent of the AC 44? Thanks.

Jim C.

[Stuart F.]

Re: 1966 327-300hp Spark Plugs

Jim;

I'll check in on this thread a little later, but right now I have a dental appointment. Still I wanted to say, I agree with the Champion alternative. I have used them for many years because since I installed an electronic ignition conversion, I don't have to change them very often as in years past with points. As such, the Champs are less likely to rust into your heads over the long stretch of time between changes. I believe they may have a better compression seal as I do know they will clean up well on the road. By that I am referring to those times when your engine may load up in summer traffic and foul a plug or two. With the champs, some highway driving seems to cure the problem where the AC's are dead. I don't mean WOT blasts to do this as this will just glaze the contaminents on permanently with either AC's or Champs.

Stu Fox

[Timothy B.]

Re: 1966 327-300hp Spark Plugs

Larry,

If you developed a skip with extended idle on a 300hp motor running AC heat range 45 it's probably time for tune up.

I will offer some of my experence and that's to do away with the points and install a Breakerless SE ignition. The engine will always run like new points and keep the plugs clean.. If you have access to a glassbeader clean those plugs and reuse. Cover the plug carefully so as to clean the porclin and tip and blow VERY good to remove any glassbeads.

I agree with Joe above, the AC44's are a good plug to use. I bought a set from someone at a swap meet for $2. and cleaned them up, they are running fine in my 300hp 67. The breakerless is one of the best improvements along with the carburetor work that I have done to that engine..

FWIW, I think your 66 has a Holley 4160 that should run pretty lean so if it's up to snuff you should be happy with your effort.

[John D.]

Re: 1966 327-300hp Spark Plugs

Larry, My guess is you have other issues instead of the spark plugs.
Nothing wrong with you using AC45. With todays corn fuel a hotter plug is not a minus factor.
If you want to stick with the points go to NAPA and buy CS786 P and the matching condenser. NAPA also has a cheap Black/copper cap RR168 that works good. (except for judging).
Spark plug wires/coil are another issue. JD

[Joe C.]

Re: 1966 327-300hp Spark Plugs

Jim;

I'll check in on this thread a little later, but right now I have a dental appointment. Still I wanted to say, I agree with the Champion alternative. I have used them for many years because since I installed an electronic ignition conversion, I don't have to change them very often as in years past with points. As such, the Champs are less likely to rust into your heads over the long stretch of time between changes. I believe they may have a better compression seal as I do know they will clean up well on the road. By that I am referring to those times when your engine may load up in summer traffic and foul a plug or two. With the champs, some highway driving seems to cure the problem where the AC's are dead. I don't mean WOT blasts to do this as this will just glaze the contaminents on permanently with either AC's or Champs.

Stu Fox

Larry, My guess is you have other issues instead of the spark plugs.
Nothing wrong with you using AC45. With todays corn fuel a hotter plug is not a minus factor.
If you want to stick with the points go to NAPA and buy CS786 P and the matching condenser. NAPA also has a cheap Black/copper cap RR168 that works good. (except for judging).
Spark plug wires/coil are another issue. JD

WOT blasts (should) run A/F ratios in the neighborhood of (about) 12.5 - 13.5:1. The range shows a cam with higher duration on the rich side, to low duration, on the lean side. Steady state cruise produces the leanest A/F ratios, and it is best to burn off (clean) plugs at steady state cruise, where the A/F ratio can approach 14.7:1 (stoichiometric) on very mild vintage engines. Modern, electronically controlled engines will cruise with mixtures leaner than stoich, because of the near perfect homogenization of the charge, and near perfect distribution.

Mister fuel injection is correctamundo! Which he can be, at times.

I also agree with Timothy about the Breakerless SE.............best improvement one can make to the engine, by far. Case in point: I had frequent issues with points bounce (which will cause misfire and foul plugs) at engine speeds over 5500. I went to the higher spring tension breaker points, which were good up to 7000 RPM, with occasional bounce/false motion/high speed plug fouling. Breakerless SE now enables consistent blasts to 7500 RPM without missing a beat. The problem with even the most accurate breaker points, is that the voltage will drop 10-20 per cent at high engine speeds, from the ideal 12KV produced at low engine speeds. What this means, is that the voltage "margin" (voltage above about 5-7 KV needed to produce a strong spark which will ignite the mixture) is reduced to the point whereby ANY deficiency in the secondary ignition system will cause a misfire.

The only drawback, is that now I really ought to install a rev limiter.

[Jim C.]

Re: 1966 327-300hp Spark Plugs

Good advice Stu. I still have the standard stock ignition. What's the Champion equivalent of the AC 44 plug?

Jim C.

[Duke W.]

Re: 1966 327-300hp Spark Plugs

AC heat range 5 plugs are best for normal driving. They won't foul in low speed traffic with lots of idling and won't overheat with occasional bursts of WOT to the redline, so your misfire is likely due to some other issue.

If judging is not an issue, I recommend the NGK B4 or Denso W14-U. These are non-resistor, equivalent heat range to the out-of-production non-resistor AC 45. and I recommend them for all OE AC 44 applications. They both have bright plated shells that won't corrode like ACs.

BTW, NGKs have been standard equipment in new Corvettes for nearly 15 years.

Duke

[Joe C.]

Re: 1966 327-300hp Spark Plugs

Good advice Stu. I still have the standard stock ignition. What's the Champion equivalent of the AC 44 plug?

Jim C.

Try this:

http://www.sparkplug-crossreference.com/index.php

[Joe L.]

Re: 1966 327-300hp Spark Plugs

Hey Joe,

What is the Champion equivalent of the AC 44? Thanks.

Jim C.

Jim-----


Champion no longer manufactures an equivalent of the AC 44 or 45. However, they do manufacture equivalents of the 44S and the 45S. These are as follows:

44S= Champion J12YC

45S= Champion RJ18YC (this is a resistor plug but it will work fine)

The extended tip plugs will work perfectly in your application and I would recommend them over the non-extended tip.